High temperature surface-combustion radiant heater



Jan. 21, 1969 E. E. STRAND 3,422,811

HIGH TEMPERATURE SURFACE-COMBUSTION RADIANT HEATER Filed Feb. 8. 1968Sheet of 5 INVENTOR: ELMER E. STRAND.

ATTORNEY Ji 2 .969 E- E. STRAND 3,422,811

HIGH TEMPERATURE SURFACE-COMBUSTION RADIANT HEATER Filed Feb. 8, 1968Sheet 2 of 5 -INVENTOR.' ELMER E. STRAND :z QLMM 29 u ATTORNEY Jan. 21;1969 E. E. STRAND 3,422,811

HIGH TEMPERATURE SURFACE-COMBUSTION RADIANT HEATER Filed Feb. 8, 1968Sheet 3 of 5 EE-312i? INVENTOR; ELMER E. STRAND- ATTORNEY.

E. E. STRAND Jan. 21, 1969 HIGH TEMPERATURE SURFACE-COMBUSTION RADIANTHEATER Filed Feb. 8, 1968 Sheet 4 INVENTOR: ELMER E. STRAND,

ATTORNEY.

E. E. STRAND Jan. 21 1969 HIGH TEMPERATURE SURFACE-COMBUSTION RADIANTHEATER Filed Feb. 8. 1968 Sheet INVENTOR. ELMER E. STRAND ATTORNEY,

United States Patent 3,422,811 HIGH TEMPERATURE SURFACE-COMBUSTIONRADIANT HEATER Elmer E. Strand, 59 E. Sunset Ave., Salt Lake City, Utah84115 Continuation-impart of application Ser. No. 555,570, June 6, 1966.This application Feb. 8, 1968, Ser. No. 704,018 U.S. Cl. 126-92 13Claims Int. Cl. F33d 11/44; F24c 3/04; F23d 13/12 ABSTRACT OF THEDISCLOSURE A surface combustion type, radiant gas heater, having aburner and reverberatory screen assembly, is provided with a reflectorthat is spaced backwardly from the screen assembly. The reflector isbacked by a cooling jacket through which a cool-ant is forced. Higherthan usual burner screen temperatures can be obtained, and the screenassembly is fabricated of materials capable of withstanding such hightemperatures. In the industrial treatment of materials, an impermeable,but thermal energy absorbing and radiating member is spaced forwardly ofthe screen assembly to seal the material being treated from the productsof combustion generated by the heater. A plurality of the heaters can becombined in mutually spaced side-by-side relationship to provideprogressive heating of the material being heated or heating of a largerexpanse of material. Olftake ducts formed between the heaters can thenform passages through which the products of combustion can be removed.

This application is a continuation-in-part of my application Ser. No.555,570, filed June 6, 1966, now abandoned.

This invention is concerned with the generation of heat of exceptionallyhigh temperature (e.g. in the neighborhood of 3000 F.) and with theapplication of such heat to useful purpose. It provides a gas-firedradiant heater that can be constructed and operated economically toproduce the desired heat and to apply such heat to a variety ofpurposes, especially the treatment of materials industrially.

Use is made of various concepts and features shown by the Mentel et a1.U.S. Patent 3,084,736 granted Apr. 9, 1963, entitled Gas-Fueled InfraredGenerator, but considerably higher temperatures are achieved withcorrespondingly increased intensity of radiated energy and withoutcontamination of the materials being treated by the accompanyingproducts of combustion. Moreover, a series of the heaters can beadvantageously utilized for the overall treatment of a broad surfacearea or for progressive heating of a material. Danger of flame flashback into the fuel feed system is greatly minimized if not completelyeliminated.

The Mentel et al. infrared generator is known as a surface combustiontype of gas burner. It utilizes a fine mesh burner screen unit, throughwhich the fuel gas is forced from a plenum chamber for combustion at theouter face of such screen in a manner that heats the screen toincandescense. A reverberator screen of relatively course mesh is spacedoutwardly from the burner screen unit, so as to act as a damper toprevent hot gases from being wiped away too rapidly and also as areflector to reverberate infrared rays back onto the burner screen,thereby building up its temperature to incandescence. A reflective,safety screen may be spaced in back of the burner screen to help preventflash back of flame into the plenum chamber and combustion of fuel gastherewithin at the relatively low temperature specified, i.e. 900 F. to1800" F.

Features of the present invention are the utilization of ice a reflectorof radiant energy rays, as the back of the plenum chamber, the provisionof a forced cooling system for such reflector, the provision of animpermeable and imperforate thermal energy absorptive and radiatingplate spaced forwardly of the reverberator screen, and the provision forleading off and venting products of combustion from between the burnerscreen and the impermeable radiating plate.

For the extremely high temperatures that are preferred with heaters ofthe invention, although not necessarily employed, the screens andradiating plate must be of a material, such as silicon-carbide orceramic coated Fiberchrome, manufactured by the Johns-ManvilleCorporation, capable of withstanding the extremely high temperaturesinvolved, but the reflector can be of any heatconductive material havinga reflective surface, e.g. polished stainless steel or polishedaluminum.

One highly useful application of the radiant heaters of this inventionis in connection with the method and apparatus of Storrs U.S. Patent No.2,809,154, granted Oct. 8, 1957, entitled, Heat Treatment of Substancesfor the Recovery of Decomposition Products. As so applied, highintensity radiant energy is projected downwardly onto material passingtherebeneath from a radiating plate shared in common by a series of theheaters. Other uses will become apparent. For example, the heaters ofthe invention can be used to dry materials, in calcined operations, orin the roasting of metallurgical ores in accordance with methods otherthan that taught by the said Storrs patent.

Some representative applications of the invention are shown in theaccompanying drawings, which illustrate the best modes presentlycontemplated of practicing the invention. Further objects and featuresof the invention will become apparent from the accompanying drawings anddetailed description that follows:

The drawings FIG. 1 represents a fragmentary top plan view, partly inhorizontal section, taken from the standpoint of the line 11 of FIG. 4,and showing a series of the radiant heaters of this invention serving asthe heating means for a material-processing retort;

FIG. 2, a corresponding bottom plan view taken from the standpoint ofthe line 2-2 of FIG. 5;

FIG. 3, a fragmentary perspective View, drawn to a. considerably largerscale, of supporting framework forming a component of one of the heatersof the series;

FIG. 4, a fragmentary end elevation drawn to a considerably larger scalethan are FIGS. 1 and 2;

FIG. 5, a longitudinal vertical section taken on the line 55 of FIG. 4;

FIG. 6, a transverse vertical section taken on the line 66 of FIG. 5 anddrawn to a still larger scale;

FIG. 7, an enlarged fragmentary view of that portion of FIG. 6 encircledby the line 7, an intermediate portion being broken out for convenienceof illustration;

FIG. 8, a side elevation view of a thermal reactor utilizing anotherembodiment of the heater of the invention;

FIG. 9, a horizontal section, taken on the line 9-9 of FIG. 8;

FIG. 10, a fragmentary, enlarged vertical section, taken on the line10-10 of FIG. 9;

FIG. 11, a fragmentary, vertical section, drawn to an even larger scalethan is FIG. 10, and taken on the line 1111 of FIGS. 9 and 10;

FIG. 12, a horizontal section, taken on the line 1212 of FIG. 10;

FIG. 13, a vertical section, taken on the line 1313 of FIG. 12;

FIG. 14, a view like FIG. 12, but showing still another form of theinvention; and

'3 FIGS. 15 and 16, vertical sections taken on the line 1515 and 16-16,respectively, of FIG. 14.

Detailed description Referring to the drawings: In the particularembodiment illustrated in FIGS. 1-7, a series of six radiant heaterunits 20, constructed in accordance with the invention, are arrangedside-by-side any event is to subjecta material to be heat-treated to theradiant heating effect of the heater units 20. It is tobe understood,however, that one or more of. such heater units can be employed in otherways for various industrial, commercial, or domestic heating purposes.

Each heater unit comprises a dual assembly of respective sets of screens24, 25, and 26, FIG. 7, and 27, FIG. 6, providing a surface-combustiontype of gas burner, such as shown by the afore-referred-to Mentel et al.Patent No. 3,084,736. Screen 24 is a safety screen, screens 25 and 26together form a burner or generator screen unit, and the screen 27 is aso-called reverberator screen, all in substantial accord with theinfrared generator of such patent, the commercial form of which ismanufactured by the C. A. Olsen Manufacturing Co., Elyn'a, Ohio, un-

der the trade designation Infralux. However, other surface-combustiontypes of burner screen construction can be employed. For example, wherethe excessively high temperatures noted above are involved, it will benecessary to utilize perforate cloth of graphite, silicon carbide, orceramic coated Fiberchrome, instead of the customary metal screen. Onesatisfactory, fine mesh carbon cloth, is that produced by theCarboiundu-m Company under the trademark Carbotex.

The two sets of screens forming the dual assembly of each heater unit 20are mounted in a supporting frame 28, see especially FIG. 3, and, forthis purpose, each set is advantageously framed by stainless steelstripping 29 that encloses the edges of the screens 24, 25, and 26together with an interposed spaced strip 30 of mild steel, and that hasa depending flange 29a to which a longitudinal edge of screen 27 issecured.

The frame 28 has longitudinal side members 28a, FIG. 3, which seat andsupport outer longitudinal edge margins of adjoining sets of screens,and transverse end members 28b, which similarly seat and support ends ofsuch sets of screens. Otherwise, the frame 28 has flue-forming side andend members 28c and 28d, respectively, joined to and upstanding from theouter lateral edges of the respective side members 28a and end members2811, respectively, and has lower transverse end members 28c, joined attheir opposite ends to depending portions of respective flueforming endmembers 28d.

The inner longitudinal edge margins of adjoining, sets of screens aresecured to and serve to support an-openended conduit 53, FIGS. 5 and 6,that provides circulation for a coolant fluid in a cooling chamber 31.

Such cooling chamber 31 and a plenum chamber 32 for the distribution ofa gaseous fuel, such as natural gas or packaged LPG, are formed abovethe sets of screens by means of and at opposite faces ofa reflectorplate 33, which is concave and preferably curved as a parabolicreflector and has its longitudinal edges connected in fluidtightrelationship with the side walls 34 of an inverted tank. The plate ispreferably stainless steel, with its reflector surface highly polished.Connections with the mild steel tank walls 34 are preferably made bywelding. Plates 35 close opposite ends of the plenum chamber 32, and thecooling tank has end walls 36 and a top wall 37, which,

4 together with sidewalls 34, completely enclose the cooling chamber 31.

A fuel gas and air mixture is introduced into plenum chamber 32 from anysuitable source byway of a supply pipe 38 and perforate distributorheader 39, which advantageously has a perforate divider plate 39aextending diagonally along its length. This makes for uniform burningconditions at the burner screens. A coolant fluid,.usually andpreferably water, is introduced to cooling-cham ber 31 through a pipe 40and discharged through a pipe 41. Although most of the heat energy isreflected by reflector 43, the provision for forced cooling, especiallyby a liquid coolant, enables operation at ultra-high temperatures. i Thescreen sets are anchored to respective flanges 44a 'of walls: 44 bymeans of bolts 42, with heat resistant gaskets 43 interposed. Followinginstallation of'the assembled screens and tank in supporting frame28,heat insulation 44 is packed into the spaced b'etween'walls34 andflue-forming walls 28c.' Opposite margins of the framed screens aresecured to the bottom of conduit 30 by screws 45, with heat resistantgaskets 46 interposed and an insulated, protective shield 47 appliedtherebelow for supporting inner longitudinal edges of the screens 27.

As is usual with surface combustion. types of gas burners, the gas fromplenum chamber 32 burns on the outer surface of each of the screens 26.Spaced below the screens is a heat absorbing and radiating plate 48that, with the reflector 33, has the effect of intensifying the radiantenergy generated by the burner screens. Screens '24, 25, and 26 arepreferably 40, 10, and 60 mesh, US. Standard, respectively, and screen27 preferably has openings inch square.

Leading from the combustion chamber 49, formed between the screens andplate 48, are flues 50 for conducting gases of combustion to disposalthrough any suitable stack (not shown). Adjoining end members 28d ofside-byside frames 28, see FIG. 1, provide for formation of the flues 50between upstanding side wall members 28c of v such frame.

The combustion chambers 49, which are in communication side-by-sidealong the length of the retort served by the several heater units 20,are preferably sealed from, the

outside atmosphere by liquid trap seals SLFI G. 5', utilizing dependingflanges 48a of plate 48. Plate 48 acts as a black body in absorbing,with great efiiciency, the radiant energy directed to it from the burnerscreens and reflector 33, until the plate 48, itself, becomes intenselyhot. Since the plenum chamber is insulated and insulation is provided'around the combustion chamber, the radiant energy absorbed by plate 48can only be emitted downwardly from the plate 48 to thematerial 23. Theretort chamber 52 containing the material 23 thus receives maximum.radiant heat energy frorn'the intensely hot plate 48, while beingcompletely separated from gases of combustion which are conducted awaywithout contacting such material. Because the gases of combustion are oflow density, they are virtually unaffected by the reverberatingthermal'energy and they are relatively cool as they are conducted away,in comparison to the more intense temperatures of the burner screen andplate 48.

In the embodiment of FIGS. 8-13, the heaters of' the invention are showngenerallyat 55. They are wedgeshaped and are mounted like spokes beneatha central exhaust stack 56 of a thermal reactor, shown generally at 57.A reactor of this type is fully shown and described in my co-pendingapplication for US. Patent, Ser. No. 704,067 filed Feb. 8, 1968.

Each heater includes a lower frame that includes a coolant circulatingsystem made up of hollow side members 58 and 59, that converge to beconnected at one of their ends by a hollow end member 60. The other endsof the side members are more widely spaced and are connected by a hollowmember 61 that has a partition 61a intermediate its length.

Spaced between end members 60 and 61 and interconnecting the sidemembers 58 and 59 are a series of intermediate, elongate, hollow members62 of triangular crosssection. Each intermediate member has its endswelded to the side members 58 and 59 such that orifices 63v and 64,through the respective side members, interconnect the interiors of theside members with the interior of the intermediate member. The members62 are arranged with their apexes downwardly and their bases spaced justslightly apart. The side walls of the triangular intermediate membersthus form reflectors to reflect radiant energy towards and through aburner screen 65, that is stretched tautly below the apexes. The burnerscreen is cerarnically bonded to the bottoms of side members 58 and 59and end members 60 and 61. Although other materials can be used, a finemesh, ceramic coated, Fiberchrome screen has been found suitable for useas the burner screen.

A closed hood 66 is fixed to the side and end members and a fitting 67in the large end of the hood overlying end member 61 is adapted to havea fuel line 68 connected thereto. A controlled ratio of gas and air canbe supplied as a fuel gas through line 68 and fitting 6 7 to hood 66, inany convenient manner.

The fuel gas entering the hood moves downwardly through the smallopenings between the bases of intermediate members 62 and through theburner screen where it is ignited at the face of the burner screen andbehind a reverberator screen 69. The reverberator screen is like thatheretofore described and has larger openings therethrough than does theburner screen. As illustrated, the reverberator screen in clampedbetween an insulating member 70 that is affixed to the bottom of theburner screen beneath the end and side members, and an angle member 71.In a reactor such as that illustrated, and shown more in detail in myaforementioned co-pending application for patent, Ser. No. 555,570, theangle member 71, at the large end of the heater, rests on a ring ofinsulation 72, FIG. 10, that is supported by a ring member 73, havinginsulation 74 on the inside thereof and an outer ore guide 750 thatserves as a facing.

A circular, impermeable and imperforate membrane member 76,corresponding to the plate 48 previously described, and made of amaterial or materials capable of absorbing and radiating heat energy butimpervious to gases of combustion, is clamped at its outer edge betweenring of insulation 72 and ring member 73 by bolts 77 that are passedthrough the ring of insulation to be threaded into a ring member 77a.Material to be heat treated, using the heaters of the invention, isspread on a screen 78 that is rotated beneath the impermeable membrane,and after it has been so treated the residue is removed. Screen 78 isstretched tautly over rods 78a that radiate out from and that rotatewith a central plate 78b. The inner edge of impermeable membrane 76 isclamped between a ring of insulation 79, on which the small end of theheater rests, and an insulating ring member 80 that is positioned on asupport plate 81, by bolts 82. An inner ore guide 75b depends fromsupport plate 81 to a point just above screen 7 8, so that it holdsmaterial to be heat treated on the screen.

The details of the screen 78, the drive means therefor, the feed meansfor feeding material onto the screen, the means for removing residuefrom the screen, and the inner and outer ore guides are all shown indetail in my co-pending application for US. patent Ser. No. 704,067filed February 8, 1968.

Gases of combustion formed by operation of the heaters cannot passthrough the impermeable membrane and are discharged upwardly throughflues or ducts defined by the outside walls of the hoods of adjacentheaters to be directed into exhaust stack 56 by a hood 83 that fits overthe heaters and that is sealed to them and to the ring of insulation 72throughout the space between the heaters. Because the gases are not verydense, they are not significantly affected by the radiant energyreverberation between the burner screen assembly, the reflector, andmembrane 76 and since they are carried away quickly after combustiontakes place they remain relatively cool. The hood 83 is sealinglyconnected to the lower end of the exhaust stack. The outer walls of theside members and hoods of adjacent heaters thus form flue-walls todirect the gases of combustion into the exhaust stack 56. If foundnecessary, to prevent heating of the coolant water, insulation 84, canbe placed against the lower frame, adjacent to the side members.Brackets 84a, suspended from the hood holds support plate 81 and theheaters resting thereon.

In practice, fuel is supplied to the interior of hood 66 through fitting67 and is thereafter distributed through the narrow spaces between thebases of intermediate members 62 and the burner screen to the combustionchamber formed between the front face of the burner screen and thereverberator screen. The adjacent, inclined faces of the intermediatemembers cooperate to form a reflective surface, corresponding to thatpreviously described, and with the burner screen to form a plenumchamber at the back side of the burner screen. As the fuel is passedthrough the narrow openings formed between the intermediate members 62it is cooled, or maintained cool, by the contact with the intermediatemembers through which water is being circulated as a coolant. Thus,there is very little, if any, danger of the fuel in the plenum chamberbeing hot enough to support flash back and the safety screen heretoforedescribed is not necessarily required.

In FIGS. 1416, there is shown another type of coolant system that can beused in lieu of the coolant system of the lower frame shown in theembodiment of FIGS. 8-13. The coolant circulating system of the lowerframe of FIGS. 14-16, is made up entirely of pipe members and, in somecases, may be more economical to construct than coolant circulatingsystem of the lower frame heretofore described. As illustrated, pipes 85and 86 serve as the side members of the frame and with pipes 87 and 88,connected at the ends thereof as the long and short end members,respectively. Intermediate, pipes 89 extend between the side members andare closely spaced so that fuel supplied through the hood will be evenlydistributed as it passes between them. The intermediate pipes are madeof a material that will carry the coolant water and that will providegood reflective surfaces that will cooperate with the reverberatorscreen 89 in heating the burner screen to incandescence and in radiatingenergy through the burner screen to the impermeable membrane 90. Themounting of the reverberator screen 89 and if impermeable membrane 90are the same as previously described in connection with the heater ofFIGS. 813.

Openings 91, through the wall of pipes 85 and 86, into each of theintermediate pipes 89, are designed to insure continuous flow of wateras a coolant, through each intermediate pipe.

Water is supplied to pipe 87 at one side of a plug 92, and is passedthrough pipes 85, 88 and 86 and each of the intermediate pipes 89,before being returned to pipe 87 to be discharged at the opposite sideof plug 92.

When the coolant system, shown in FIGS. 14-16, is used, the exteriorsurfaces of curved walls of adjacent intermediate pipes cooperate toform a reflective surface that functions to reflect heat energy in thesame manner as do the reflective surfaces heretofore described.

Obviously, a lower frame utilizing a combination of pipes and otherspecially designed members, such as are shown in FIGS. 813, could alsobe used.

It should also be apparent that the overall shape of the heaters can bechanged, as required for a heating operation. For example, they can bemade rectangular or circular rather than wedge-shaped, as disclosed.Also, a plurality of heaters can be arranged other than as shown, sothat material to be heat treated can be passed beneath them, or so thatthey can be moved into position to heat such material. If only oneheater is required for an operation, it can be made of any desired sizeor shape.

Experience with the radiant heaters of this invention has shown that anexceptionally high conversion of available B.t.u. input to radiantenergy output that can easily be put to useful purpose, is accomplished.

Although preferred forms of my apparatus have been herein disclosed, itis to be understood that the present disclosure is made by way ofexample and that variations are possible without departing from thehereinafter claimed subject matter I regard as my invention.

I claim:

1. A gas-fired, high temperature radiant heater, comprising an assemblyof screens forming a surface combustion type of gas burner;

means including a reflector having a substantially concave forward faceforming with said screens a plenum chamber behind and in operativecommunication with said assembly of screens;

means for introducing fuel gas into said plenum chamber, so fuel gaswill pass into the screen for surface combustion forwardly and outsideof said chamber; and

means including a chamber behind said reflector for forcing a coolant inintimate contact with the back of said reflector.

2. A radiant heater in accordance with claim 1, wherein the coolant is aliquid.

3. A radiant heater in accordance with claim 1, wherein the screens areof a highly heat resistant material, such as silicon carbide, for ultrahigh temperature operation.

4. A radiant heater in accordance with claim 1, wherein there isadditionally provided an imperforate, heat-radiating member spacedforwardly of the assembly of screens, so as to separate the combustionarea of the heater from an area of heat application.

5. A radiant heater in accordance with claim 4, wherein theheat-radiating member has an area substantially commensurate wth thescreen area, so as to define a combustion chamber between it and thescreens.

6. A radiant heater in accordance with claim 5, wherein fiues forproducts of combustion lead from the combustion chamber and said chamberis otherwise closed.

7. A radiant heater in accordance with claim 5, wherein there areadditionally provided walls defining a retort chamber within the area ofheat application, for the treatment of materials.

8. A Iradiant heater in accordance with claim 1, wherein a perforatetube is provided in the plenum chamber in communication with the meansfor introducing fuel gas thereinto, as a distributor for said fuel gas.

9. A gas-fired, high temperature radiant heater, comprising an assemblyof screens forming a surface combustion type of gas burner; l

a reflector having at least one reflective surface spaced behind theassembly of screens and arranged to reflect energy back toward the saidscreens, said reflector surface forming with the screens a plenumchamber;

means for introducing fuel gas into said plenum chamber whereby fuel gaswill pass into the screens for surface combustion forwardly and outsideof said chamber; and

means for forcing a coolant into intimate contact with the back of saidreflective surface.

10. A gas-fired, high temperature, radiant heater according to claim 9,further including an impermeable, heat-absorbing and radiating memberspaced forwardly of the assembly of screens and forming with the saidassembly of screens, at one side of the impermeable member, a combustionchamber wherein the fuel gas is burned, the opposite side of theimpermeable member being adapted to have heat radiate therefrom to anarea of heat application.

11. A gas-fired, high temperature, radiant heater according to claim 10,further including flue means connected into the combustion chamber tocarry away gases of combustion formed during the burning of the fuelgas.

12. A gas-fired, high temperature, radiant heater, according to claim 1,wherein the reflector comprises closely spaced, hollow elements throughwhich the coolant is adapted to be circulated, each said element havinga reflective surface; and

means for circulating said coolant through the said hollow elements.

13. A gas-fired, high temperature, radiant heater according to claim 12,wherein the means for introducing fuel gas into the plenum chambercomprises a hood, extending over the hollow elements; and

conduit means for directing said fuel gas into the hood,

whereby it is distributed through the spaces between the hollow elementsto the plenum chamber.

No references cited.

FREDERICK KETTERER, Primary Examiner.

U.S. Cl. X.R. 431-

